Surface mining operations are generally employed to excavate an ore deposit that is found near the surface of an ore body. Such ore deposits are usually covered by an overburden of rock, soil, and/or plant matter, which may be removed prior to commencing mining operations. The remaining ore deposit may then be excavated and transported to a plant for processing to remove commercially useful products. The ore deposit may comprise an oil sand deposit from which hydrocarbon products may be extracted, for example.
In general, the excavated ore will include sized ore portions having a size suitable for processing and oversize ore portions that are too large for processing. Separation of the oversize ore portions from sized ore portions may be performed by screening the excavated ore through a screen mesh having openings sized to permit passage of sized ore portions through the screen while preventing oversize ore portions from passing through the screen. The oversize ore portions may be discarded and/or crushed to produce sized ore. One problem associated with such screening is that the screen mesh is prone to blockage.
Roller screens have also been used to screen ore. The roller screen has a plurality of adjacently located rollers, each roller having a plurality of screening disks mounted in spaced apart relation on a shaft. The screening disks intermesh with screening disks on an adjacent roller of the roller screen to define interstices for permitting passage of sized ore portions through the roller screen. The rollers are coupled to a rotational drive to cause the rollers to rotate, thereby clearing blockages that may occur while screening the ore.
In the example of an oil sand ore deposit, such as the Northern Alberta oil sands, the ore deposit comprises about 70 to about 90 percent by weight of mineral solids including sand and clay, about 1 to about 10 percent by weight of water, and a bitumen or oil film. The bitumen may be present in amounts ranging from a trace amount up to as much as 20 percent by weight. Due to the highly viscous nature of bitumen, when excavated some of the ore may remain as clumps of oversize ore that requires sizing to produce a sized ore feed suitable for processing. Due to the northerly geographic location of many oil sands deposits, the ore may also be frozen making sizing of the ore more difficult.